1. Field of the Invention
This invention relates to a cantilever chip for use in a scanning probe microscope.
2. Description of the Related Art
An Atomic Force Microscope (AFM) has been proposed and put to practical use, as a microscope which utilizes a technique such as a servo technique for use in a Scanning Tunneling Microscope (STM) invented by Bennig, Roller, etc., in order to measure, with atomic-order accuracy, an insulating sample which is difficult to measure by means of the STM.
The AFM has a structure similar to the STM, and is categorized as a scanning probe microscope. In the AFM, a cantilever having a free end provided with a sharp projection (probe portion) is made to approach a sample, and the probe portion is moved along the sample, thereby electrically and optically measuring displacement of the cantilever due to interaction between an atom at the tip of the probe portion and an atom on the surface of the sample. Data relating to each point of the sample surface is obtained and processed in time sequence, thus obtaining three-dimensional data as to unevenness of the sample surface, etc.
Since an SiO.sub.2 cantilever chip made as a result of application of a semiconductor IC manufacturing process was proposed in Japanese Application, Physics, 62(1987)2599, "Atomic Resolution Imaging of a Nonconductor by Atomic Force Microscope" (invented by Thomas R. Albrecht and Calvin F. Quate), it has been considered that a cantilever obtained by utilizing such a process is suitable for use as a scanning probe microscope cantilever, because it can be made with micron-order accuracy so as to have high image reproductivity, and can be manufactured at low cost by way of a batch process.
For example, a cantilever formed by a silicon nitride film in place of a silicon oxide film is available in the market. This cantilever has a length of 50 to 200 .mu.m, a thickness of 0.5 to 1 .mu.m, and in the shape of a triangle or rectangle having an inner portion removed. Further, the cantilever has characteristics such as a spring constant of 1 to 0.1N/m, and a resonance frequency of 10 to 50 kHz. The spring constant k and a resonance frequency .omega. are given by the following equations: EQU k=Et.sup.3 w/4L.sup.3 ( 1) EQU .omega.=0.162(E/.rho.).sup.1/2 t/L.sup.2 ( 2)
where E represents Young's modulus, t the thickness of a cantilever, L the length of the same, and .rho. the density of the same.
FIGS. 22 to 28 show an example of a cantilever chip made as a result of application of a semiconductor IC manufacturing process. As is shown in the figures, the cantilever chip has a triangular cantilever portion 202 having an inner portion removed, and a probe 212 provided on a tip portion of the cantilever portion 202. The cantilever chip is made by forming a silicon nitride film of a predetermined shape to provide a cantilever portion 202 and a support portion 204, and then attaching the support portion 204 to a hold substrate 206. It is preferable that the alignment end 208 of the support portion 204 be aligned with the side end face 210 of the hold substrate 206, as shown in FIGS. 22 and 23. Actually, however, there is a strong possibility of a cantilever chip being produced in which the alignment end 208 is not aligned with the side end face 210, as shown in FIGS. 24 to 27. Although in the case shown in FIGS. 24 and 25, the cantilever portion 202 is relatively short, the characteristics of the cantilever chip are substantially identical to those of the chip shown in FIGS. 22 and 23. On the other hand, in the case shown in FIGS. 26 and 27, a portion 204a projecting from the side end face 210 of the hold substrate 206 greatly affects the cantilever chip, thereby making its characteristics differ from the desired ones of the cantilever chip shown in FIGS. 22 and 23. Accordingly, such a cantilever as shown in FIGS. 26 and 27 cannot be put to practical use.
In addition, a cantilever chip produced in the above-described process generally has a plurality of cantilever portions, and is used at the time of measurement, with unneeded cantilever portions broken off. In the cantilever chip of FIGS. 26 and 27, a cantilever portion 202B to be used for measurement may be cracked, as indicated by the one-dot-chain line in FIG. 28, when an unneeded cantilever portion 202A is broken off. In the worst case, all the cantilever portions may be broken off from the side end face 210 of the hold substrate.